1. Field of Use
This invention relates generally to improved apparatus and methods for forming a crater in a bed of material beneath a body of water.
In particular, the improved apparatus includes an improved submersible crater sink mechanism, control means therefor and pump means for use therewith. The improved methods relate to operating the improved crater sink mechanism.
2. Description of the Prior Art
The prior art contains various apparatuses and mechanisms for use in underwater dredging systems to form a crater in a bed of material underlying a body of water.
As prior art FIGS. 11 and 12 hereof show, some dredging systems employ a prior art submersible jet pump which is located at an underwater site where a crater is to be formed and is connected by hoses to a clear water supply pump and to a booster discharge pump, both pumps usually located on a nearby shore. A typical prior art jet pump takes the form of a tubular housing defining a chamber having a constricted, nozzle-like clear water inlet port at one end, an expanded, larger diameter discharge port at its opposite end and a suction port in a side thereof intermediate the other two ports. A suction tube for ingesting dredged material has one end connected to the suction port and has its opposite end disposed against the bed of material. The discharge port is connected to the discharge booster pump. The clear water inlet port is supplied with clear water at high pressure from the water supply pump. Thus, the chamber functions like a venturi tube in that the increase in velocity of the clear water flowing therethrough is accompanied by a proportional decrease in hydraulic pressure. This results in fluidized dredged material, i.e. a mixture of material from the bed and ambient water, flowing into and through the suction tube and into the chamber wherein it mixes with clear water and this mixture is expelled through the discharge port to the discharge booster pump for ultimate delivery to a disposal site. Such prior art jet pumps rely solely on the negative pressure differential between the fluid in the chamber and the body of water in which the jet pump is submerged to effect ingestion of dredged material into the chamber and are very inefficient, requiring several pumps and a large power input to the clear water pump and booster pumps for effective dredging operations, i.e. on the order of 500 hp or greater, for example.
Use of the prior art jet pump hereinbefore described (and other types of suction pumps) is accompanied by several problems. If, for example, in order to pump sand the inlet (suction) hose is merely lowered to the bed of material, several possibilities can occur; (1) the pump will have near zero production, pumping water only; (2) the pump will move a little sand at first and then taper off to near zero production thereafter; (3) the pump will have a high production rate to start with and then taper off to near zero output thereafter; (4) the pump will start with little production and increase steadily until the system plugs up; (5) the pump will not produce at the proper ratio of sand to water to ensure proper mixture flow. Items 1 through 3 above result in serious economic consequences from lost production. Item 4 causes very serious mechanical and logistical problems and the pump will be in a self-destruct mode and vast amounts of time and effort will be required to unplug the lines. Regarding item 5, the proper ratio does not occur as a natural event. The dredging industry accomplishes this feat by means of many accessories to support and move the dredge pump and, ultimately, the suction end thereof. However, this will still not get the job done without the direction of a human operator who increases or decreases the percentage of solids by manipulating the suction of the pump. Left unattended, the system will revert to conditions 1 through 3. The problem of line plugging is of paramount importance when the pipe line is buried, such as under inlets. Great expense and engineering expertise are required to surmount this event.
My U.S. Pat. No. 4,574,501 issued Mar. 11, 1986 entitled "In-Place Underwater Dredging Apparatus of the Crater Sink Type" discloses in-place underwater dredging apparatus for dredging solid particulate matter from an underwater site to clear a channel thereat, mixing it with dirty or dredge water, pumping the mixture from the site by means of a built-in pump and discharging it at a remote location.
My prior art apparatus comprises a housing shaped like an inverted "T" formed by a horizontal tube open at both ends and an upstanding vertical tube connected intermediate the ends which defines a mixing chamber. A hydraulically driven pump is mounted on the upper end of the vertical tube and has a discharge conduit for conducting the mixture to the remote location. Motor-driven rotatable augers are disposed in opposite ends of the horizontal tube and extend generally laterally outwardly from the lower end of the upstanding tube. The augers operate to deliver solid particulate matter at a selected rate to the mixing chamber in the upstanding tube. A dirty or dredge water inlet port is provided in the horizontal tube of the housing intermediate the inner end of the augers and is connected to a dirty water inlet pipe. During a dredging operation the pump draws a mixture comprising solid particulate material from the augers and dirty water entering the dredge water inlet port through the upstanding tube and discharges the mixture at the remote location. The dirty water fluidizes the material fed from the augers, thereby enabling it to be more easily handled by the pump. A clear water intake pipe, including a shut-off valve, is connected to a clear water inlet port located near the upper end of the upstanding tube for admitting clear water thereby insuring that the apparatus is clean before starting and can be purged after use. However, the valve is closed during a dredging operation and no clear water is admitted to the chamber during dredging.
In my prior art apparatus the ends of the horizontal tube extend radially outwardly from the lower end of the vertical tube in a generally horizontal direction and the apparatus, when submerged, is designed and constructed to rest in a fixed location on the bed beneath the body of water and can be started whenever desirable, i.e. after solids have accumulated to a certain depth on the bed, to thereby again clear the site to the desired level. The apparatus remains at a fixed depth, i.e. on the original bed surface, and does not sink deeper as dredging occurs. Generally, the apparatus is installed at the site while the area is clean and is positioned at its desired depth. Thereafter, the apparatus can be left in place (in situ) and operated whenever the solid particulate matter rises to a level above the floor which necessitates its removal. A stabilizing mounting structure including metal plates are secured to and extend transversely across the bottom of the horizontal tube of the housing so as to provide stability and prevent its shifting, tilting or sinking downward below its desired fixed depth.
My prior art apparatus contemplates a hydraulic fluid power source which can be located remotely from the site to be dredged, as for example, up on the adjacent shore or on a barge. This power source has hydraulic fluid lines connecting its fluid pressure pump with the hydraulic pump mounted on top of the upstanding tube of the apparatus and also with a hydraulic motor that drives the auger screws.